As semiconductor devices are scaled down to submicron dimensions, planarization technology becomes increasingly important, both during the fabrication of the device and for the formation of multi-level interconnects and wiring. Chemical-mechanical planarization (CMP) has recently emerged as a promising technique for achieving a high degree of planarization for submicron very large integrated circuit fabrication.
CMP is a process of smoothing surfaces with the combination of chemical and mechanical forces. It can be thought of as a hybrid of chemical etching and free abrasive polishing. The process uses an abrasive and corrosive chemical slurry (commonly a colloid) in conjunction with a polishing pad and retaining platen, typically of a greater diameter than the wafer. The pad and wafer are pressed together by a dynamic polishing head and held in place by a plastic retaining platen. The dynamic polishing head is rotated with different axes of rotation (i.e., not concentric). This removes material and tends to even out any irregular topography, making the wafer flat or planar. This may be necessary in order to set up the wafer for the formation of additional circuit elements. For example, this might be necessary in order to bring the entire surface within the depth of field of a photolithography system, or to selectively remove material based on its position. Typical depth-of-field requirements are down to Angstrom levels.